When system software is upgraded in an existing passive optical network (Passive Optical Network, PON) system, a manner of independently upgrading an optical line terminal (Optical Line Terminal, OLT) and an optical network terminal (Optical Network Terminal, ONT) is used, and generally, the ONT is first upgraded and then the OLT is upgraded. When the ONT is upgraded, a service interruption may be caused due to reset. When the OLT is upgraded, a service interruption may also be caused due to reset. In this case, at least two service interruptions are successively caused in an entire process of upgrading the PON system, where a time of the service interruptions is a sum of a time of the ONT resetting and a time of the OLT resetting. Therefore, a relatively large quantity of service interruptions and a relatively long time of the interruptions degrade user experience.